1. Field of the Invention
The present invention is directed generally to a window baffle. More specifically, the present invention is directed to a window baffle in an active laser system that absorbs and scatters energy, such as from secondary reflections, while causing minimal impact to system performance.
2. Background Information
Segmented windows exhibit desirable aerodynamic performance characteristics as well as low observable capabilities. In order to achieve these qualities, a window, such as a Forward Looking Infrared Radar (FLIR) window, is generally not flat and facing forward, but rather has multiple facets or segments. However, at least two effects have impacted the use of multiple segmented windows.
First, the seams at the interface of each segment in a segmented window deleteriously impact the optical performance. The effects of the seams can be minimized through the use of small joints and by engineering, for example, engineering the window to take advantage of optical properties such as Snell""s Law of Refraction to reduce the impact on optical performance.
Second, the effects of secondary reflections from one face to another can be significant. For example, in systems with active laser elements, the use of a segmented window design has been shown to cause stray energy loss in excess of the eye-safe requirement for that laser. Secondary reflections from a laser source can be significantly powerful even with an anti-reflective (AR) coating.
Attempts to attenuate the secondary reflections in such systems have been made. For example, U.S. Pat. No. 6,042,650 discloses a baffle system to block radiation from a laser source due to reflections and scattering. Similarly, U.S. Pat. No. 4,542,963 discloses the use of baffles to prevent stray radiation from the reflections on the side of a telescope.
Previous baffle systems have suffered from negatively impacting the available Field of View (FOV) of the optical system in which they are used. This occurs when, for example, the window is physically blocked to prevent stray energy from leaving the system. Designs of previous window baffles have attempted to balance the required need for reduced internal reflections in a system with the need to maximize the FOV. In general, this balancing has resulted in at least some reduction in the FOV.
Therefore, it is desirable to reduce internal reflections in an optical system while maintaining the maximum FOV of the optical system.
An exemplary embodiment of a window baffle assembly has a multi-element segmented window having a first surface adapted to receive at least one wavelength of radiation from an optical system, a baffle housing positioned proximate at least a portion of the first surface of the segmented window, and a plurality of baffle elements each affixed between positions on the baffle housing and offset from the first surface of the window. Each baffle element comprises a leading edge and an opposing trailing edge, the leading edge oriented toward the first surface of the window. The plurality of baffle elements are in a Field of View of the optical system at an operational angle.
The surface of the baffle elements are adapted to absorb at least a portion of the energy of the radiation and oriented to scatter the radiation. In an exemplary embodiment, the surface of the baffle element has a desired surface roughness to scatter the radiation. In another exemplary embodiment, the trailing edge of the baffle elements are oriented to point toward a central point of the optical system.
A portion of the leading edge of each baffle element is affixed to the baffle housing. In an exemplary embodiment, the window baffle assembly has a reinforcing element joined to each of the baffle elements and to the baffle housing. The reinforcing element can be joined to each baffle element between the positions at which the baffle elements are affixed to the baffle housing.
An exemplary embodiment of a window baffle assembly has a window having a first surface and a second surface, the first surface opposing an aperture of an optical system for transmitting and receiving radiation and a plurality of baffle elements arranged on the first surface of the window such that at least a first wavelength of radiation is transmitted from the optical system through the baffle elements and the window and at least a second wavelength is transmitted through the window and the baffle elements to the optical system. At least a portion of the baffle elements are in a Field of View of the optical system and each has a trailing edge oriented toward a central point of the optical system such that the baffle elements scatter or absorb at least a portion of the first wavelength and a portion of the second wavelength.
A method of manufacturing a window baffle assembly comprises the steps of determining a plurality of reflections associated with a first wavelength of radiation, forming a plurality of baffle elements having a length from a leading edge to a trailing edge, and positioning a plurality of baffle elements proximate a first surface of at least a portion of a window such that the trailing edge of each baffle element overlaps the leading edge of an adjacent baffle element by at least a predetermined percentage of the distance from the leading edge to the trailing edge. The plurality of baffle elements are positioned such that each is oriented to scatter incident radiation while a mean transmission loss is less than 25%. The method can further comprise a step of joining a center section of each of the plurality of baffle elements with a reinforcing element such that a deflection distance of any one baffle element is no greater than a predetermined value. Still further, the method can comprise a step of affixing the baffle elements to a baffle housing about a perimeter of the window.
The surface of the baffle elements can be adapted to absorb at least a portion of the energy of the radiation incident thereon. For example, the surface can be coated with an energy absorbing coating and/or roughened to a predetermined surface roughness.